Tuesday, April 2, 2013

Interaction levels between computers on the Internet

Zero level
It is connected with the physical environment which transmits a signal. This level represents intermediaries (cables, radio lines, etc.), connecting final devices. There is a set of different types and types of cables: ekranirovanny and neekranirovanny, twisted couples, coaxial cables, cables on the basis of optical fibers, etc.

First level
Level which includes physical aspects of transfer of binary information on the communication line. In details describes, for example, tension, frequencies, the nature of the transferring environment. Maintenance of communication and reception-transmission of a bit stream is imputed to this level a duty. At this level the faultlessness is desirable, but it isn't required.

Second level
Channel level provides communication of data, i.e. faultless transfer of blocks of data (called by shots or frames, frame) through level 1 which by transfer can distort data. This level has to define the beginning and the shot end in a bit stream, to form shots or sequences of data of the 1st level, to include procedure of verification of mistakes and their correction. This level (and only it) operates with such elements, as bit sequences, methods of copying and markers. It bears responsibility for the correct data transmission (packages) on sites between directly connected elements of a network. Provides management of access to the transfer environment.

Third level
Network level uses the opportunities given to it by level 2 for ensuring communication of two any points in a network. Any, unreliable adjacent. At the same level routing is made, and also processing of addresses and demultiplexing is carried out. The main function of the software at this level is selection of information of a source, its transformation to packages and the correct transfer to an appointment point. There are two basic various modes of work of network level – a method of virtual channels and a method of datagrams.

Fourth level
Transport level regulates transfer of packages of messages between the processes which are carried out in computers of a network, finishes the data transmission organization. Collects information from blocks in its former look. Or, expects a response (confirmation from the destination), correctness of delivery and addressing checks and repeats a parcel if the response didn't come.
Transport level hides any details and data transmission problems from all highest levels, provides standard interaction of level being above it with a reception-transmission irrespective of concrete technical realization of this transfer.

Fifth level
Session level coordinates interaction of communicating users, operates with them, restores abnormally ended sessions. The same level is responsible for network cartography – it transforms regional (domain) computer names to numerical addresses, and vice versa. It coordinates not computers and devices, and processes in a network, supports their interaction – operates communication sessions between processes of applied level.

Sixth level
Level of data presentation deals with syntax and semantics of the transmitted data, i.e. mutual understanding of two being reported computers how they represent here is established and understand when receiving the transmitted data. Here such problems, for example, as code conversion of text information and images, compression and unpacking, support of network file systems, abstract structures of data, etc. are solved.

Seventh level
Applied level provides the interface between the user and a network, makes available for the person various services. At this level five applied services – a file transfer, remote terminal access, electronic transmission of messages, service of the directory and management of a network are realized, at least.

To each level of interaction there corresponds a set of protocols (i.e. I ruled interactions).

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